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<h2>Time Synchronization</h2>

<p>BWCTL works best when the clocks of the clients and servers are synchronized. If the hosts are not synchronized, they might try to begin tests at different times.</p>

<p>
<a href="http://www.ntp.org/">NTP</a> is a protocol used to synchronize a
computer's clock to clocks available over a network. The NTP software is
available for, and often times, included with many operating systems. Most Unix
systems use the reference implementation of the software, and the example
included with this howto is geared to that version. 
</p>
<p>
ntp.org has some <a href="http://twiki.ntp.org/bin/view/Support/SelectingOffsiteNTPServers">advice</a>
for selecting NTP servers. However, there are some general rules of thumb to
follow for NTP configuration. The NTP configuration should include between 4
and 7 NTP clocks with which it will try to synchronize. By including this number of
servers, the NTP software can make better decisions about which clocks are
accurate and who it should trust for time data. The NTP servers should be in
close proximity to the host, though this is not a hard requirement. Ideally,
the network paths to the servers should differ as much as possible from each
other.
</p>
<p>
There are a large number of public NTP servers. There's a list available at <a
href="http://support.ntp.org/bin/view/Servers/WebHome">http://support.ntp.org/bin/view/Servers/WebHome</a>.
</p>
<p>
Internet2 maintains a set of NTP servers that can be used if the host is
connected to the Internet2 network.
<ul>
	<li>owamp.atla.net.internet2.edu - Atlanta, GA</li>
	<li>owamp.chic.net.internet2.edu - Chicago, IL</li>
	<li>owamp.hous.net.internet2.edu - Houston, TX</li>
	<li>owamp.losa.net.internet2.edu - Los Angeles, CA</li>
	<li>owamp.kans.net.internet2.edu - Kansas City, MO</li>
	<li>owamp.salt.net.internet2.edu - Salt Lake City, UT</li>
	<li>owamp.newy.net.internet2.edu - New York, NY</li>
</ul>
</p>

<h3>Example NTP /etc/ntp.conf file</h3>
<pre>
# /etc/ntp.conf, configuration for ntpd
logfile /var/log/ntpd
driftfile /var/lib/ntp/ntp.drift
statistics loopstats peerstats clockstats
filgen loopstats file loopstats type day enable
filgen peerstats file peerstats type day enable
filgen clockstats file clockstats type day enable

server owamp.chic.net.internet2.edu iburst
server owamp.hous.net.internet2.edu iburst
server owamp.kans.net.internet2.edu iburst
server owamp.losa.net.internet2.edu iburst
server owamp.newy.net.internet2.edu iburst
</pre>
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